As a method of synthesizing phosphonate esters along with the formation of a carbon-phosphorus bond, in general, the method in which the corresponding halide is substituted with triatkylphosphite has been known. However, with this method, different types of halide compounds are formed along with the reaction and a large volume of by-products are generated. In addition, halides newly generated through the reaction additionally react with the trialkylphophite, so that a disadvantage is that a large volume of sub-products is created. Therefore, the method of the prior art cannot be said to be an industrially advantageous method.